Manufacture of bonded and inflated sheet laminations



Dec. 6, 1966 E. w. AGIN ETAL 3,289,231

MANUFACTURE OF BONDED AND INFLATED SHEET LAMINATIONS Filed July 9, 1963 5 Sheets-Sheet 1 INVENTORS ERNEST W. AGIN BOYD D. CAVE RICHARD F. HAFER THEIR ATTORNEYS Dec. 6, 1966 E. w. A GIN ETAL 3,239,231

MANUFACTURE OF BONDED AND INFLATED SHEET LAMINATIONS Filed- July 9. less 5 Sheets-Sheet 2 N 9C 5 m 5m mm w W TA V. S A! NMFJFY wmL A W 0 m m mam Mm m H Wm H mm D; m

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Dec. 6, 1966 MANUFACTURE OF BONDED AND INFLATED SHEET LAMINATIONS Filed July 9, 1963 5 Sheets-Sheet 34 i @915 c wl MN w/A A moN w mwm i 1mm Y &/ A B Iv [MH all M OTwE R? k o- 0% am mm. m mm; 2 mi mm maven mi 7 7% A% r w J 7 x Z m OE N \RL $33K mT 0N1 NQJ II mTwE wTwE y x g law L k. 25% 10E @ON.

I THEIR ATTORNEYS United States Patent ()flice 3,29,281 Patented Dec. 6, 1966 3,289,281 MANUFACTURE OF BQNDED AND INFLATED SHEET LAMINATTONS Ernest W. Agin, Boyd 1). Cave, and Richard F. Hater, Chesterfield County, Va., assignors to Reynolds Metals Company, Richmond, Va., a corporation of Delaware Filed Italy 9, 1963, Ser. No. 293,654 13 Claims. (Cl. 29--]l57.3)

This invention relates to bonded and inflated thin sheet laminations which may be used as heat exchangers and the like.

Composite passageway panels heretofore have been made by bonding together adjacent surfaces of two or more stacked sheets of relatively soft aluminum-containing metallic material. Thereafter, a tube structure or pattern has been inflated in the bond zone between the two sheets. This procedure has produced a metallic sheet lamination having the tube structure disposed between the sheets of the lamination. Heat exchange fluid, either liquid or gaseous, has been circulated within the tube structure of the lamination to heat or cool the heat exchanger and its environment. Usually relatively soft aluminum-containing metallic materials or alloys have been used in the manufacture of such heat exchangers. Some of the relatively soft aluminumcontaining metallic materials or alloys heretofore used have a minimum aluminum content in the order of 99%. Aluminum alloys of the 1000 series, such as aluminum alloy 1100, for example, have been used with satisfactory results. These relatively soft alloys lend themselves to inflation to produce the tube patterns by inflating the lamination with fluids under pressures in the order of 3,000 p.s.i.

Heat exchangers made of such relatively soft aluminum alloys are satisfactory from a heat exchange standpoint when such heat exchangers are not required to bear relatively heavy loads or bending stresses during normal use. Such prior art heat exchangers, however, are relatively weak in load bearing characteristics, and, moreover, certain objectionable imperfections frequently enter into the manufacturing processes of such heat exchangers. Further, the tube passageways in the heat exchangers and the bond between the sheets of the lamination are only capable of withstanding internal test pressures of approximately 100 to 500 psi.

With recent requirements that tube structures be capable of withstanding internal pressures of 600 psi. or more, and be capable of bearing relatively heavy loads which produce bending and other stresses during normal use, it has become necessary to produce tube structures from stronger materials than heretofore used. Such materials include, for example, sheets of aluminum alloys of the 2000, 3000, 5000, and 6000 series. When such alloys are used in producing tube structures, however,

certain problems arise which are not encountered inv using the softer aluminum-containing materials. In order to get a suflicient bond between harder aluminum alloy sheets, which bond will prevent separation of the sheets under internal test pressures of at least 600 p.s.i. applied to the tube structure, the alloy frequently becomes work hardened to the extent that the sheets are rendered substantially non-formable. Thus, an attempt to inflate the bonded sheets between configurated die components by peeling the sheets apart results in rupture of the walls of the tube structure under the pressure of the inflating fluid. If a softer or more formable alloy cannot be used, then the work hardened alloy lamination must be treated to increase its elongation properties, as set forth more fully hereinafter. Still, if the alloy sheets of the lamination become too soft or workable when treated, then a necking problem is .encountered during inflation thereof, as set forth more fully hereinafter, which renders the inflated tube structure defective and useless for all practical purposes. It has been found too that an inflating pressure of between about 8,000 p.s.i. and 15,000 psi. is required to separate bonded sheets of work hardenable aluminum alloy and form the sheets by expansion thereof into a die cavity, where the strength of the bond and sheet strength are such that the inflated lamination will withstand an internal pressure of at least 600 psi.

Thus, it will be appreciated that the present invention is concerned with the production of bonded and inflated laminated tube structures capable of resisting considerable stress and withstanding substantial internal pressures. Further, the present invention concerns the use of harder aluminum alloys than heretofore used in making laminated tube structures, and overcomes the problems encountered in making laminated tube structures using such alloys where the tube structure must be capable of withstanding the internal pressure set forth above. More particularly, the invention is concerned with methods of producing tube structures from a lamination including at least one work hardenable aluminum alloy sheet of such hardness that the sheet is substantially non-formable without rupture thereof. wherein a stronger bond is required between the sheets than in similar structures heretofore produced, and wherein the strength of the work hardenable aluminum alloy sheet of the lamination together with the stronger bond necessitates the use of inflating pressures considerably higher than pressures required when softer materials are used. Still further, the present invention concerns the control of the strength of the bond relative to the strength of the aluminum alloy sheet and the strength of the alloy sheet relative to the formability of the sheet, whereby the alloy sheet can be separated from an. adjacent sheet of the lamination and formed by expansion into an adjacent die cavity without rupture to produce a tube structure having the design characteristics of strength mentioned hereinbefore. The control of these relationships is of utmost importance in the production of tube structures having a tube passageway free from undesirable constrictions or restrictions in the walls thereof.

Necking, as used herein, denotes one or more undesired inward restrictions or constrictions in a tube pattern. These restrictions or constrictions are produced by inward bending of the walls of a tube of the pattern, and are of a character such that they cannot be removed by any reasonably satisfactory method. For example, they cannot be removed by increasing the inflating pressures of the inflating fluid of the manufacturing process, because any such attempted removal generally results in the bursting of the side walls of the tube structures.

streams of inflating fluid converge head on with each other in a manner to produce an irreversible sharp curve or uninflatable constriction at such head on zone. Restrictions also are frequently produced in a tube passageway wherein inflating fluid is moving in one direction only as opposed to moving in converging directions. These latter restrictions are referred to as dead ends since they generally prevent further inflation of the laminate.

In accordance with the present invention, the formation of irreversible bends or constrictions in an inflated tube structure is substantially reduced by causing the tube Walls of the tube structure to travel in a sharp and acute angular forwardly moving wedge formation ahead of the inflating fluid during an inflating operation. The wedge formation advantageously protects the tube walls from being rolled over, so to speak, by the advancing inflating fluid and thus prevents the formation of restrictions or constrictions in the inflated article. The thickness of the sheet material, the hardness of the alloy, the height of the inflation, the strength of the bond zone, and the pressure of the inflating fluid are of a character to produce the wedge formation ahead of the inflating fluid, and the forwardly moving wedge formation provides for progressively peeling the laminate along the path of a die cavity in a manner whereby irreversible inward bends or restrictions are avoided. With certain die cavity configurations, the wedge formation is capable of meeting a similar on-coming wedge formation which results in the production of a relatively long, gentle, wave-swell-like, reversible formation which is straightened by the sidewise inflation pressure of said inflation fluid, without the production of irreversible inward bends or restrictions in the tube pattern.

Accordingly, it is one of the objects of this invention to provide a method of producing a heat exchanger or other tube structure having one or more of the features herein disclosed.

Another object of this invention is to provide apparatus and articles suitable for producing a heat exchanger or other tube structure having one or more of the features herein disclosed.

Another object of this invention is to provide a heat exchanger having one or more of the features herein disclosed.

Other objects, advantages, and details of the invention are apparent from this description and the accompanying drawings, in which:

FIGURE 1 is a diagrammatic representation of an apparatus and method for practicing this invention.

FIGURE 2 is a plan view of a typical heat exchanger which may be made according to this invention.

FIGURE 3 is a cross-sectional view of an inflated heat exchanger taken along the lines 33 of FIGURES 2 and 4 and showing portions of the forming dies.

FIGURE 4 is a cross section along the line 4-4 of FIGURE 3, slightly above the lower sheet of the lamination.

FIGURE 5 is a cross section along line 5-5 of FIG- URE 4 and showing portions of the forming dies.

FIGURE 6 is a cross section along line 66 of FIG- URE 4.

FIGURE 7 is an enlargement of the portion of FIG- URE 3 which is indicated by the dotted rectangle 7.

FIGURE 8 is an enlargement of the portion of FIG- URE 5 which is indicated by the dotted rectangle 8.

FIGURE 9 is an enlarged diagrammatic cross section of a typical approaching collision wave action of this invention produced by oppositely moving expansion wedges which may occur anywhere in the heat exchanger, such as indicated at random to be at line 99 of FIGURE 4.

FIGURE 10 is a view similar to FIGURE 9 and showing a later stage of the wave action.

FIGURE 11 is a view similar to FIGURES 8 and 9 and showing the final stage of the wave action.

FIGURE 12 is a cross section along line 1l212 of FIGURE 9.

FIGURE 13 is a cross section along line 13-13 of FIGURE 9.

FIGURE 14 is a cross section along line 1414 of FIGURE 10.

FIGURE 15 is a diagrammatic view corresponding to FIGURE 9 but showing a typical action which frequently occurs in a manufacturing step of a prior construction.

FIGURE 16 is a view showing a later stage of the action of FIGURE 15.

FIGURE 17 is a view showing the final, irreversible constriction forming action of FIGURE 15.

FIGURES 18-20 are views corresponding to FIG- URES 1517 and showing another type of similar unde- 4 sirable and irreversible necking action of previous constructions.

FIGURE 21 is a view similar to FIGURE 7, showing another embodiment.

FIGURE 22 is an isometric view of a partially inflated laminate, showing a form of restriction which is avoided by the present invention.

The procedure illustrated in FIGURE 1 may be used to practice this invention. As shown in FIGURE 1, unclad work hardenable aluminum alloy sheet material may first be dry annealed as indicated at furnace 30. A plurality of sheets 32, of desired oversize, trim dimension of sheet surface, are maintained in the furnace by handing, stacking, belt transmission, etc., so they may be properly annealed, cooled and delivered to the wire brush cleaning apparatus 34, where a wire brushing action or other cleaning action is provided to clean off the oxide and possibly to roughen the surface of the sheets, in a desirable manner, at least on the bond sides of said sheets.

The term unclad is intended to apply to a sheet of aluminum alloy, which is not covered or clad with a layer of softer and more pure aluminum material. According to this invention, the bonded sides of the outer sheets of the lamination may be substantially uncladded.

Two of these sheets, or more, may be stacked together, with unclad sides adjacent each other, as indicated at 36, and may have their leading edges secured together, as by spot welding at 38, so that this leading edge may be fed into rolls later to be described. In addition, if desired, a band 40 of stop weld material maybe previously painted on one of the inner surfaces of one of the sheets, so that an inflating tube inlet may be produced between the sheets such as at point 40, which may be readily opened by an opening tool or an inflating needle.

The laminations 36 are then placed in a furnace 42, so they may be heated to a temperature suitable to produce the desired strength of bond in the bonding zone between unclad sides of the sheets when the sheets are hot rolled at this temperature. The heated laminate 36 is then rolled at 44 between rolls 46, with the rolling action regulated to produce a reduction in the lamination 36 which will assure adequate bonding of the sheets.

For bonding sheets of a given aluminum alloy, the hot rolling temperature and the percent of reduction control the bond characteristics between the sheets 32. Accordingly, these conditions are controlled during the rolling process in accordance with the alloy of the sheets to produce a bond of sufficient strength to provide for the desirable inflating action which prevent constriction formation, as elsewhere described. In this respect, the strength of the bond produced is less than the strength of the sheets themselves. Still, the bond is strong enough to withstand considerable internal pressure, such as that of heat exchange fluid likely to be applied during use of the lamination as a heat exchanger or the like.

The laminate leaving the rolls 46 is moved to a second set of rolls 5t and passes therebetween for further reduc tion. The temperature of the laminate is somewhat lower during passage between rolls 50. The reduction in thickness of the laminate during the second rolling step is less than the reduction during passage between rolls 46, and there is no material change in the physical properties of the laminate, except the change of thickness and length. The bonding strength and other characteristics of the laminate are not materially changed during the passage through the rolls 5%).

The laminate 36 may then be hardened, if desired, by being worked or cold rolled in the cold rolls 52. During the passage through cold T011 52, the laminate may be reduced to a final gauge thickness. The cold rolling introduces work hardening from any condition of hardness the lamination may have had after passage through the rolls 50.

The laminate may now be opened along one of its edges for the purpose of inflation. For example, an opening punch or tool 54 may be punched into the edge of the lamination Where the stop weld material 40 had previously been introduced between the sheets of the lamination. By this procedure an opening may be punched which is of suflicient size later to receive the inflation needle 66. Suitable punch and needle constructions are now well known, and hence are not further described.

The lamination 36 may also be trimmed and otherwise made ready for the inflation procedure.

The laminate 36 may then be inflated in the configurated die assembly 56 which has one die 58 with a substantially flat surface, and with the other die 60 having grooves, configurations or convolutions 62 cut into its face to produce the tubing pattern in the upper sheet elsewhere described in connection with the laminate which is to be formed.

The laminate then is inflated through the needle 66 using an inflating fluid which may be oil, water, or gas. If water is used, the same may be distilled Water, so that any remnant of water which does not later drain from the tubing may be evaporated without leaving any substantial residue.

The inflation fluid may be pumped by any suitable pump 68 which has its inlet 69 connected to the fluid reservoir 70 and its outlet 7 connected to the needle 66. A suitable gauge, or automatic controller, or the like, 72 may be provided to govern the introduction and/ or pressure of inflation fluid into the lamination. A reciprocating pump has been illustrated by way of example, but any type of suitable pump may be used, as is obvious.

After inflation, the inflated lamination may be removed from the die and the inflation fluid may be removed by draining and/or heatinn and slightly boiling. Suitable well known additional treatments may be provided for the inflated lamination, to prepare it for use as a refrigerator evaporator, a heater, or as a cooler of any other type.

It is to be understood that in the procedure described above the second and third rolling operations set forth may be varied to some extent Without materially affecting the strength of bond achieved during the first rolling operation in the hot mill. In this respect, the third or cold rolling step may be omitted, or the second hot rolling step may be omitted. Further, the amount of reduction of thickness of the laminate during the rolling operations may be varied in accordance with bond characteristics to be achieved.

The strength of the bond between the sheets of the laminate is determined primarily by the percent reduction of the laminate thickness during the first hot rolling operation. It has been found that a reduction of between 50% and 60% is required during this rolling operation in order to get a bond of minimum suitability with the Work hardenable alloys mentioned herein. As the percent of reduction increases, so does the strength of the bond. The bond characteristics of diiferent alloys, of course, are not the same, and, accordingly, the percent of reduction producing a desirable bond will vary with the particular alloy being used.

In working with stronger aluminum alloys such as alloy 3004-, for example, the rolling and reduction re quired to achieve an adequate bond between the sheets of a lamination often result in work hardening the alloy of the sheets to a substantially non-formable condition, as mentioned hereinbefore. In accordance with the present invention, this condition can be alleviated, when encountered, without destroying the relationship between the bond strength and sheet strength. In this respect, the formability of the aluminum alloy sheets can be increased to the extent necessary to permit inflation of the lamination without rupture of the sheet and, at the same time, the srength of the sheets can be maintained greater than the strength of the bond therebetween. More particularly, it has been found that partial annealing following the rolling operation, if properly controlled, produces a lam- .inate wherein the sheets have elongation properties permitting forming of the sheets by expanison into a die cavity under the pressure of an inflating fluid. Still, the strength of the sheets is such that they peel apart in the bond Zone in a manner whereby the walls of a tube passage being formed by the advancing inflating fluid produce a sharp and acute angular forwardly moving wedge formation ahead of the fluid, which wedge formaton is essential to prevent constriction defects in the tube structure. it will be appreciated that the annealing step described differs from ordinary annealing intermediate conventional metal working steps, since the present operation involves controlling the temper condition of the metal sheet in relation to the bond strength of the laminate and other factors.

The amount of annealing, of course, varies with the characteristics of the lamination and the size of the tube passageway to be produced by inflating the lamination. For example, it has been found that the partial annealing must be such as to permit elongation of the sheet material in the range of 10% or more, when making wide x .200" high passageways in a lamination having a gauge thickness of approximately after rolling. The following table sets forth the hardness to which certain aluminum alloys used in producing tube structures of the above dimensions in accordance with the present invention must be annealed, and the range of elongation of the annealed laminations.

Percent Elonga- Alloy Hardness tion, As" strip TBS-H36 10-12 If the lamination is partially annealed as outlined above, then the sheet material can be expanded into a die cavity Without rupture, and since the strength of the sheet is maintained greater than the strength of the bond between the sheets, peeling of the sheets is achieved during inflation and objectionable necking is avoided. Thus, it will be appreciated that a proper balance between strength and elongation properties of the sheet material must be maintained, and at the same time a proper relationship of sheet strength to bond strength must be maintained.

The selection of a particular alloy to be used is determined primarily by the design requirements of the tube structure to be produced. In this respect, the sheets of the selected alloy must be capable of being hot rolled and reduced in thickness to provide a bond capable of withstanding the design internal pressure requirement without delaminating the sheets of the product. At the same time, the sheets of the lamination must be capable of being partially annealed, if need be, to a hardness which will permit elongation of the sheet material to the extent necessary to expand the sheet material into a die cavity by pressure of the inflating fluid, but which will not weaken the strength of the sheet material to a strength less than that of the bond.

Aluminum alloy 3004 has certain characteristics which permit the inflation procedure to be advantageously produced according to this invention when the tube structure being produced is to be capable of withstanding an internal pressure of 600 p.s.i. or more.

Aluminum alloy 3004 has a chemical composition substantially as follows: silicon up to 0.30%; iron up to 0.7%; copper up to 0.25%; manganese 10-15%; magnesium 0.81.3%; zinc up to 0.25%; others up to 0.05% each, up to 0.15% total; balance aluminum.

When sheets of aluminum alloy 3004- are hot rolled at a temperature above the recrystallization temperature of the alloy and reduced in thickness an amount suflicient to produce a bond therebetween capable of withstanding an internal working pressure of 600 p.s.i. or more after the laminate is inflated to produce a tube structure, the sheets become hardened to such an extent that expansion of the sheets into a die cavity during inflation generally results in rupture of the walls of the tube passageway being formed between the sheets. On the other hand, if the sheets are fully annealed to remove the work hardening effect, the alloy becomes too soft relative to the bond strength and inflation cannot be carried out successfully. If the lamination be partially annealed to approximately quarter hardness after roll bonding, however, the elongation properties at such hardness permit expansion of the sheets without rupture. Moreover, the strength of the sheets is thereby maintained stronger than the bond between the sheets whereby the lamination has the proper balanct between bond, elongation, and hardness to permit the sheets to peel and produce the wedge formation and the wave-swell action described hereinafter to prevent the frequent constriction formation of prior constructions.

The following specific examples are illustrative of the practice of the present invention with regard to particular aluminum alloys and their use in producing tube structures having a requirement to withstand an internal pressure of approximately 600 p.s.i.

Example 1 Two sheets of .140 inch aluminum alloy 3004 were cut to a predetermined blank size and cleaned by wire brush to remove oxide and roughen the surfaces thereof. A surface of one of the clean sheets Was then printed with stop-weld material in an area to define an entrance between the sheets when bonded, and the two sheets were then staked together and heated to a temperature between 900 F. and 1000 F. The sheets were then hot rolled in a 4-I-Ii hot mill having a work roll of 18 inch diameter. The rolling temperature was approximately 920 F. and the laminate was reduced from a thickness of .280" to .070 amounting to a reduction of 75%. The laminate was then rolled again in a second hot mill at a temperature of approximately 600 F. which represents a natural temperature drop in the laminate between the successive roll mills. The second hot mill had a work roll of 21" diameter, and the laminate thickness was reduced from .070" to a finish gauge of .060, amounting to a reduction of 14.3%. The laminate was then flattened by rolling, and annealed to the A hard range (H32) by heating for approximately /2 hour at 600 F. to improve the elongation properties of the laminate. The laminate was cut to predetermined size and the entrance between the sheet was opened to receive an inflating needle. The laminate was then placed between die components designed to produce a two-side expanded structure, an inflation needle was inserted, and the die closed. A hold down force of approximately 1500 tons was applied to the die components, this force being in excess of the total expansion force to be applied internally of the laminate. Inflation fluid was then injected to a maximum pressure of 15,000 p.s.i., which pressure was suflicient to separate the sheets in the bond zone and form the tube structure. The formed structure was then removed from the die, drained, sheared to final size and dehydrated. The tube structure was found to be clear of deleterious restrictions, and an internal test pressure in excess of 600 p.s.i. was applied to the structure without rupture of the walls of the structure or separation of the sheets. The tube passageways produced in this instance were x .200" passages.

Example II Two .125" sheets of 3004 aluminum alloy were prepared for rolling in the same manner as set forth in Example I. The rolling procedure in this instance was otherwise the same as in Example I with respect to the mills used and the temperatures of the two hot rolling passes; however, during the first hot roll pass, the laminate was reduced in thickness from .250 to .070", amounting to a reduction of 72%. During the second hot roll pass, the laminate was reduced from .070" to a final gauge thickness of .060, a reduction of 14.3%. Following rolling, the laminate was annealed to A1 hardness (H32) and inflated in the manner set forth in Example I. The inflated tube structure so produced showed no evidence of undesirable constrictions or restrictions; however, it was determined upon injection of internal test pressure that the bond in this instance was not as strong as the bond achieved by the practice outlined in Example 1, although the structure withstood a test pressure of 600 psi. The tube passageways produced were /5" x .200" passages.

Example HI Two sheets of .125 gauge aluminum alloy 3004 were prepared for rolling as in Examples I and II. The laminate was then rolled in the first hot mill of Example I at the same temperature. Reduction of the laminate in the first mill was from a thickness of .250" to .090", amounting to a reduction of 64%. In the second hot roll mill, at the temperature disclosed in Example I, the laminate was reduced from .090 to .065", amounting to a reduction of 30%. The laminate was then passed through a cold mill at room temperature, the cold mill having a work roll of 21" diameter. The laminate was reduced in the cold mill from a thickness of .065 to a final gauge thickness of .060, amounting to a reduction of 10%. The laminate was then annealed to A hardness (H32) and inflated in the manner set forth in Examples I and II. The inflated article evidenced no constrictions or restrictions and when subjected to internal test pressure withstood pressure in excess or" 600 psi. The tube passageways produced were x .200" passages.

The amount of reduction during the first hot roll operation in Example III was considerably less than that of Examples I and II in order to reduce the load on the mill. It will be noted, however, that the amount of reduction during the second hot roll operation was increased considerably over that of the same rolling operations of Examples I and II, and that the total reduction during the hot roll passes of Example III, namely 74%, closely corresponds with the reduction during the first hot roll pass of Examples I and II.

It is believe-d that the advantages of the present invention will be more readily apparent upon consideration of the prior techniques of making tube structures, and the causes of constriction formation frequently encountered in the use of earlier techniques. FIGURES 15 through 22, inclusive, illustrate the manner in which irreversible bends or constrictions are formed during inflation of laminates in accordance with such prior practices.

FIGURES 15, 16 and 17 show the type of action which takes place in prior manufacturing operations and which are likely to produce an irreversible constriction in the tubing of the lamination which cannot be blown out by the inflation fluid without bursting the side walls of the lamination.

With the prior constructions, as shown in FIGURES 15-17, the large angles 132A and 134A of the walls C and 120D as indicated in FIGURE 15 cause the slanting walls 120C and 120D to approach each other in such a manner that when they arrive near each other as at 120E and 120E, FIGURE 17, the curvature of the wall produced at that point has produced a wall elongation which is so long and roundabout that the inflation pressure cannot push the curve back into the straight-line position. The round curved wall 120E, 120E is so much longer than the straight wall construction that it is impossible for the inflating fiuid to straighten out or contract the wall 120E, 120E. The inflation pressure cannot contract the wall 120E, 1201? into a straight-line position, as is obvious from an inspection of FIGURE 17. The irreversible constriction produced at 120E, 120E has been permanently formed, and cannot be inflated outward.

9 In this manner an undesirable restriction is produced in the tubing.

The constriction produced in FIGURES 18 through 20 is somewhat similar to that illustrated in FIGURES through 17. In this case, reverse bends 120G and 120H are produced as walls of the tube come nearer and nearer, as illustrated in FIGURES 18 and 19. The resulting neck is almost circular, as indicated at 1201 in FIGURE 20, where the inflation pressure is hopelessly unable to inflate the neck 1201 outward into a straight line.

FIGURE 22 illustrates a further form of restriction produced in prior manufacturing operations. In this respect, a laminate comprised of sheets 130 and 131 is placed between die components for inflating the sheet 130 into a die cavity in the adjacent die component. In this instance, the intended tube path extends inwardly from an edge of the laminate as indicated by the numeral 132. Such a path may or may not be of the character wherein inflating fluid can approach a given point from opposite directions. In any event, the restriction formed in this instance is a dead end restriction which occurs before the structure has been fully inflated, and prevents further inflation. In this respect, the strength of the bond between sheets 130 and 131 is greater than the strength of sheet 130, whereby the wall 133 of the partial tube formation is caused to curve sharply into the die cavity by the force of the inflating fluid and produce a restriction which prevents inflation of the laminate. By practice of the present invention, such dead ending" is prevented by the wedge formation described herein, whereby sheets of the laminate peel apart progressively along the tube path so that the advancing wall of the tube path slopes gently throughout inflation of the laminate.

In accordance with this invention, the tube walls ahead of the inflating streams are caused to travel in sharp and acute angular forwardly moving wedge formations. Thus, where oppositely moving inflating streams converge head on, these wedges approach each other with their sharp edges toward each other. When these sharp edges meet each other in a head on zone, they produce a relatively long, gentle, wave-swell-like, reversible formation in the tube wall which is of a character to yield to the sidewise inflation pressure in a manner to straighten the tube wall. These wedges, accordingly, do not produce the irreversible sharp curve or neck of previous constructions.

The strength of the bond zone, the strength of the tube wall, the formability of the sheet material, and the height of the inflation are coordinated by the bonding, annealing, and inflating procedures of this invention as previously set forth to produce the sharp and acute angular wedge formations which approach one another in a manner whereby this gently, wave-swell-like, reversible formation is produced.

The relatively long, gentle, wave-swell-like, reversible formation of the tube wall above described may be compared, for convenience and illustration only, to the long, gentle, wave-like, reversible formation of a single wave motion or vibration in a taut string or cable which extends between two stationary supports. In such a cable, a substantial movement or vibration sidewise at the center of the span produces only an infinitesimal stretch in the length of the cable, which stretch is reversible. The cable may vibrate or be moved sidewise at the center with a considerable amplitude, and yet it can be restored to its straight line position as long as the curve produced is a long, gentle, wave-like, reversible formation.

A similar action takes place in the side wall of the tube formation, according to this invention, and such side wall may be restored to its original condition in a similar manner.

FIGURES 2 through 14, inclusive, show a typical laminated heat exchanger which may be produced according to the procedure of FIGURE 1. Further, FIGURES 2 through 14 illustrate the wedge formation mentioned above whereby inflation is achieved without the production of constrictions of the character described.

Certain directional adjectives are used for brevity of description in this disclosure, such as upper, lower, side wise, etc., but it is to be understood that such descriptive adjectives are used for convenience of description only and are not intended to limit the invention to the particular directions so described, since the invention may be used with the parts in other directions.

For convenience, sometimes one of the sheets 32 shown in FIGURES 2 through 14 is designated as 32A while another sheet 32 is designated as 323. The laminate shown in FIGURES 2 through 14 corresponds to the laminate 36 of FIGURE 1. The upper die 60 of FIGURES 2 through 14 may be the same as die 60 of FIGURE 1 while the lower die 53 of FIGURES 2 through 14 may correspond to the die 58 of FIGURE 1. The illustrations in FIGURES 2 through 14 are the actions which may take place during the inflation step illustrated at 56 in FIGURE 1.

In FIGURES 2 through 14, an inlet passage is the passage which was produced by the tool 54 and inflation needle 66 of FIGURE 1. The end of passage 80 may be connected to a header 82 which in turn is connected to branch tubes 84 which in turn are connected at their other ends to another header 86. This produces a twosheet lamination with a tube construction or net-work or pattern which is illustrated as typical only and which may be of any other desired configuration and which may be produced by the inflation step 56 of FIGURE 1.

Certain members of FIGURE 1 are designated by reference numerals which are repeated in FIGURES 2 through 14 with capital letters following, and such designations are intended to imply that the parts are the same or similar, as is obvious.

The die configuration which forms the header 86, FIG- URES 4- and 6, is indicated by the reference numerals 62A in FIGURE 6. This configuration may be connected with a series of air-escape passages 83, to permit the escape of any entrapped air between the upper sheet 32A and the die 60.

If desired, the headers R2 and 86 may have the same cross-sectional configuration as the passageways 84, although it is to be understood that any and all of the passageways may have different heights, curvature, etc. as desired.

Openings 91, FIGURE 2, may be made in the sheets 32A and 32B of the lamination 36 beyond the tube pattern. These openings 91 may receive locating pins, not shown, in die 58 for example, properly to locate the lamination 36 on the die. Also openings 91 may be used to hang the sheets or laminations in the furnaces, etc.

FIGURE 7 shows an enlarged cross section typical of any of the passageways such as headers 82 and 86 or the passageways 84, and is specifically indicaed to be an enlargement at the rectangle 7 of FIGURE 3..

In FIGURE 7, the distance 92 may be .375 inch. The radius 94 may be .125 inch and the distance 96 may be .125 inch. The downwardly concave curvature 98 may merge with another upwardly concave curvature 100 which has a radius 102, which may be also .125 inch in length. The mergence of the curvatures 98 and 100 may take place substantially midway between the summit 104 and the lowest plane 106 of the die 60.

The continuous curvature produced by the curves of the radii 94 and 102 are such that they prevent any sharp bends in the configuration of the die and the passageways and thus tend to prevent bursting along the edges of the tubing.

The continuous and reverse curvature, such as illustrated in FIGURE 7, also aids in preventing necking during inflation.

The shape of the inlet passageway 80' is such that it may be produced by a relatively simple tool 54 and which may accept a needle of the same general configuration with a tight fit as the same may be fitted and wedged into the opening 80.

In FIGURE 8 the distance 108 may be .375 inch. The distance 110 may be .062 inch. The angle 112 may be 45 and the small curvatures 114 may have a radius of .031 inch.

In inflating the tube patterns of the heat exchangers herein disclosed, both prior and according to this invention, the inflating fluid may circulate in various directions while it is inflating the passageways in the lamination. In view of the convoluted type of passageway construction generally used, it is almost certain that the inflation fluid will meander while inflating the lamination and will have branches which eventually approach each other in opposite directions, to produce head-on collisions such as illustrated in FIGURES 9 through 20.

Just where such branches produce such head-on collisions is not always certain, as much depends on the accidental speeds of the inflation fluid, the localized curvature, and many other factors. Hence a cross-section line 99 has been adopted in FIGURE 4 and has been chosen at random to indicate a possible location of such headon collision.

FIGURES 9 through 14 illustrate the relatively long, gentle, wave-swell-like reversible formations of this invention in the tube wall 120 which have been compared, for convenience and illustration only, to the long, gentle, wave-like reversible formation of a single wave motion in a taut string or cable which extends between two stationary supports. The tube wall 20 of FIGURE 9 may be considered similar to such a cable, and the places indicated by the reference numerals 122 and 1.24 may be considered as the supports of the cable. FIGURE 9 shows the inflation wedges 126 as approaching each other, but not having quite met. These wedges are produced by the oppositely moving inflation fluid streams indicated by the arrows 128 and 130. When the wedges 126 meet by a slight movement toward each other, to meet at the cross-section line 13-13, then the similarity to the taut cable becomes substantially identical. At that time there is a sharp and acute angle 132 meeting head-on another oncoming sharp and acute angle 134 which produces the wedges 126 and thus form the relatively long, gentle, wave-swell-like, reversible formation which yields to the lateral component inflation pressure which is exerted along the arrow 136. The inflation pressure indicated by arrow 136 pushes the tube wall 120 upwardly as shown at 120A in FIGURE and finally straightens the wall 120 substantially horizontally as shown at 120B in FIGURE 11. Because of the long sweeping curve along the wall 120 of the tube, shown in initial stages in FIGURE 9, the force of the arrow 136 easily pushes up and moves the wall up with a tremendous wedge action. There is practically no contraction of the wall 120 necessary in order to push it up since the length of the Wall 120 in FIGURE 9 is only negligibly longer than the length of the wall in FIGURES 10 and 11 because of the long gentle contour of the curve. The gently tapered wedge formation results from controlling the bond strength relative to sheet tensile strength as previously pointed out herein.

FIGURE 21 shows another construction for the cross section of the tubing to be made according to this invention. The dies 60A and 58A are substantially similar to the dies disclosed in connection with FIGURES 1 through 14. However, the height 96A, which corresponds to the height 96 of FIGURE 7, is only .062 inch. The length 92A is .34375 inch. The radius 94A, which corresponds to the radius 94 of FIGURE 7, is 7 of an inch in length. The radius 102A of the reverse bend or curve 100A is also 7 of an inch in length. The reverse bends meet substantially half way between the lowest and highest parts of the lower face of die 60A.

This construction may be used when the area of the tube 12 need not be as large as in the other embodiment. The sheets may be of the same material and thickness as sheets 32 of FIGURE 1. This type of construction may also be used for an inlet and may be used in lieu of FIGURE 8, if desired.

Thus, applicants have provided a highly satisfactory method of producing inflated tube structures from laminations of relatively hard aluminum alloys, which tube structures, especially heat exchanger structures, advantageously are capable of withstanding internal working pressures considerably higher than similar structures heretofore produced. More particularly, by maintaining a proper balance between bond strength and sheet strength, and at the same time between sheet strength and sheet formability, tube passageways can be formed by the advancing inflating fluid without a steep almost right angular relationship occurring between the tube walls, which would prevent progressive peeling apart of the sheets or produce a constriction between oppositely approaching inflating fluid streams. In this respect the tube walls quite advantageously are maintained in a sharp acute angular relationship during inflation as a result of the proper balances mentioned above which are achieved by bonding and annealing procedures prior to inflation.

Although considerable emphasis has been placed herein on the fact that the laminate is comprised of two or more sheets of the same alloy, or two or more sheets of the same initial thickness, it is to be clearly understood that the laminate can be, of sheets of different alloys or diflerent metals, so long as the desired bond can be achieved between the sheets to allow peeling thereof ahead of the wedge formation during inflation, and provided the proper balance can be maintained between sheet strength and formability. Further, it is to be understood that only one sheet of a laminate need expand into a die cavity relative to the adjacent sheet, and that each sheet may expand into an adjacent die cavity relative to the other sheet.

Since many possible embodiments of the invention may be made and many possible changes may be made in the embodiments herein set forth, it will be distinctly understood that all matter described herein is to be interpreted as illustration and not as a limitation.

What is claimed is:

ll. The method of producing a bonded and inflated lamination having a tubular passageway capable of withstanding substantial internal working pressure, comprising the steps of providing two sheets of material at least one of which is a work hardenable aluminum alloy sheet, bonding opposing surfaces of said sheets in a bond zone therebetween and controlling said bonding to produce a laminate having a bond in said zone of less strength than the strength of said aluminum alloy sheet yet of such strength that said sheets will not delaminate during normal use of the lamination, said aluminum alloy sheet of the laminate being in work hardened condition, partially annealing the work hardened sheet to approximately quarter hardness, positioning the laminate between die components of a die assembly wherein at least one of said die components has a tube pattern die cavity defining the desired passageway configuration and disposing said aluminum alloy sheet adjacent said die cavity, introducing an inflating fluid under pressure between said sheets of the laminate to separate said sheets along said bond zone and expand said aluminum alloy sheet into said tube pattern die cavity, whereby the strength and elongation characteristic of said aluminum alloy sheet relative to the strength of said bond providing for said sheets in separating to produce a sharp acute angular forwardly moving wedge formation ahead of said inflating fluid substantially to prevent the formation of restrictions in said aluminum alloy sheet during inflation.

2. The method of producing a bonded and inflated lamination having a tubular passageway capable of withstanding substantial internal working pressure, comprising the steps of providing two sheets of metallic material at least one of which is a work hardenable aluminum alloy sheet, bonding opposing surfaces of said sheets in a bond zone therebetween by rolling said sheets to produce a laminate having a bond in said zone of less strength than the strength of said aluminum alloy sheet yet of such strength that said sheets will not delaminate during normal use of the lamination, cold rolling the bonded laminated to finished gauge, partially annealing said aluminum alloy sheet to approximately quarter hardness, positioning the laminate between die components of a die assembly wherein at least one of said die components has a tube pattern die cavity defining the desired passageway configuration and disposing said aluminum alloy sheet adjacent said die cavity, introducing an inflating fluid under pressure between said sheets of the laminate to separate said sheets along said bond zone and expand said aluminum alloy sheet into said tube pattern die cavity, the strength and elongation characteristic of said aluminum alloy sheet relative to the strength of said bond providing for said sheets in separating to produce a sharp acute angular forwardly moving wedge formation ahead of said inflating fluid substantially to prevent the formation of restrictions in said aluminum alloy sheet during inflation.

3. The method of producing a bonded and inflated thin sheet lamination having a tubular passageway capable of withstanding substantial internal working pressure, comprising the steps of providing two sheets of aluminum alloy material, including a first sheet of work hardenable aluminum alloy, hot rolling said sheets face to face at a temperature above the recrystallization temperature of said work hardenable alloy and controlling the percent reduction of said first sheet to produce a bond in a bond zone between the sheets, said bond being of less strength than the strength of said first sheet yet of such strength that said sheets will not delaminate upon introduction therebetween in the resultant tubular passageway of fluid at a pressure corresponding to at least 600 psi, in a wide passageway, cold working the bonded laminate, partially annealing said first sheet to render the sheet expandable into a die cavity defining the desired passageway configuration without rupture of said sheet and yet maintain the strength of said first sheet greater than said bond strength, positioning said sheets between die components of a die assembly wherein at least one of said die components has a tube pattern die cavity as aforesaid and disposing said first sheet adjacent said one die component, introducing an inflating fluid under pressure between said sheets to separate said sheets along said bond zone and expand said first sheet into said tube pattern die cavity of said one die component, the strength and elongation characteristic of said one sheet relative to the strength of said bond providing for said sheets in separating to produce a sharp acute angular forwardly moving wedge formation ahead of said inflating fluid substantially to prevent the formation of restrictions in said one sheet during inflation.

4. In the method of producing a laminated tube structure of the character having a tubular passageway produced by bonding two sheets of material together to produce a bond zone therebetween and thereafter separating said sheets by introducing a fluid therebetween under pressure to expand at least one of said sheets into a tube pattern die cavity defining the desired passageway configuration, which die cavity is provided in a die component adjacent the one sheet, the improvement which comprises providing two sheets of metallic material including a first sheet of work hardenable aluminum alloy, passing said sheets through a set of work rolls and rolling said sheets under pressure to provide a laminate having a bond of less strength than the strength of said first sheet yet of such strength that said sheets will not delaminate during normal use of the lamination upon introduction of pressure therebetween in the resultant tubular passageway, cold working the laminate, partially annealing said first sheet to render the said sheet expandable into a tube patern die cavity defining the desired passageway configuration without rupture of said sheet and yet maintain the strength of said first sheet greater than said bond strength, whereby when said sheets are separated along said bond zone by inflating fluid under pressure the strength of said bond relative to the strength of said first sheet provides for said sheets to produce a sharp acute angular forwardly moving wedge formation ahead of said fluid to prevent the formation of restrictions in the walls of said tubular passageway.

5. The method of producing a bonded lamination adapted for inflation to provide an interior passageway system, comprising the steps of providing two sheets of metallic material at least one of which is a work hardenable aluminum alloy sheet, bonding said sheets in a bond zone therebetween by passing said sheets through a set of work rolls and rolling said sheets under pressure to provide a laminate having a bond in said zone of less strength than the strength of said aluminum alloy sheet yet of such strength that said sheets will not delaminate during normal use of the lamination upon introduction in the resultant passageway system of fluid at a pressure corresponding to at least 600 psi. in a wide passageway, cold working the laminate to an extent that at least said aluminum alloy sheet becomes work hardened to a substantially non-formable condition for inflation purposes, and partially annealing the laminate to render said work hardened aluminum alloy formable while maintaining its strength greater than the strength of the bond.

6. The method of producing a bonded and inflated aluminum alloy laminated tube structure having a tubular passageway capable of withstanding substantial internal working pressure, comprising the steps of providing two sheets of a work hardenable aluminum alloy, hot rolling said sheets face to face at a temperature above the recrystallization temperature of the alloy and under pressure sufficient to reduce the composite thickness of said sheets at least 50% thus to bond said sheets in a bond zone therebetween and provide a laminate having a bond strength less than the strength of said sheets yet of such strength that said sheets will not delarninate upon introduction therebetween in the resultant tubular passageway of fluid at a pressure corresponding to at least 600 p.s.-i. in a x .200 passageway of a two-side expanded lamination, rolling the laminate at a temperature below said hot rolling temperature and under pressure to reduce said sheets to a thickness of approximately 25% the original thickness of said sheets prior to hot rolling, said la-rnin'ate becoming work hardened in the. course thereof, partially annealing said sheets to render the alloy formable and yet maintain the strength of said sheets greater than the strength of the bond between the sheets, positioning the laminate between die components of a die assembly wherein at least one of said die components has a tube patter-n die cavity, introducing an inflating fluid under pressure between said sheets of the laminate to separate said sheets along said bond zone and expand at least the one of said sheets adjacent said one die component into said tube pattern die cavity thereof, said partial annealing providing for said expansion of the laminate without rupture of the expanded sheet thereof, and said bond strength providing for separation of said sheets along said bond zone in a manner whereby said sheets produce a sharp and acute angular forwardly moving wedge formation ahead of said inflating fluid substantially to prevent the formation of restrictions in the walls of said tubular passageways d-uring inflation.

7. The method of producing a bonded and inflated aluminum alloy lamination of the character formed by inflating a lamination between die components of a die 

1. THE METHOD OF PRODUCING A BONDED AND INFLATED LAMINATION HAVING A TUBULAR PASSAGEWAY CAPABLE OF WITHSTANDING SUBSTANTIAL INTERNAL WORKING PRESSURE, COMPRISING THE STEPS OF PROVIDING TWO SHEETS OF MATERIAL AT LEAST ONE OF WHICH IS A WORK HARDENABLE ALUMINUM ALLOY SHEET, BONDING OPPOSING SURFACES OF SAID SHEETS IN A BOND ZONE THEREBETWEEN AND CONTROLLING SAID BONDING TO PRODUCE A LAMINATE HAVING A BOND IN SAID ZONE OF LESS STRENGTH THAN THE STRENGTH OF SAID ALUMNIUM ALLOY SHEET YET OF SUCH STRENGTH THAT SAID SHEETS WILL NOT DELAMINATE DURING NORMAL USE OF THE LAMINATION, SAID ALUMINUM ALLOY SHEET OF THE LAMINATE BEING IN WORK HARDENED CONDITION, PARTIALLY ANNEALING THE WORK HARDENED SHEET TO APPROXIMATELY QUATER HARDNESS, POSITIONING THE LAMINATE BETWEEN DIE COMPONENTS OF A DIE ASSEMBLY WHEREIN AT LEAST ONE OF SAID DIE COMPONENTS HAS A TUBE PATTERN DIE CAVITY DEFINING THE DESIRED PASSAGEWAY CONFIGURATION AND DISPOSING SAID ALUMINUM ALLOY SHEET ADJACENT SAID DIE CAVITY, INTRODUCING AN INFLATING FLUID UNDER PRESSURE BETWEEN SAID SHEETS OF THE LAMINATE TO SEPARATE SAID SHEETS ALONG SAID BOND ZONE AND EXPAND SAID ALUMINUM ALLOY SHEET INTO SAID TUBE PATTERN DIE CAVITY, WHEREBY THE STRENGTH AND ELONGATION CHARACTERISTIC OF SAID ALUMINUM ALLOY SHEET RELATIVE TO THE STRENGTH OF SAID BOND PROVIDING FOR SAID SHEETS IN SEPARATING TO PRODUCE A SHARP ACUTE ANGULAR FORWARDLY MOVING WEDGE FORMATION AHEAD OF SAID INFLATING FLUID SUBSTANTIALLY TO PREVENT THE FORMATION OF RESTRICTIONS IN SAID ALUMINUM ALLOY SHEET DURING INFLATION. 